Field of the Invention
The present invention relates to a manganese-cobalt composite hydroxide and a process for producing the same, a positive electrode active material and a process for producing the same, and a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a manganese-cobalt composite hydroxide as a precursor of a lithium-manganese-cobalt composite oxide for use as a positive electrode active material in a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery and a process for producing the same, a positive electrode active material and a process for producing the same with the use of the manganese-cobalt composite hydroxide as a precursor, and a non-aqueous electrolyte secondary battery using the positive electrode active material. It is to be noted that this application claims priority based on Japanese Patent Application No. 2014-133399 filed in Japan on Jun. 27, 2014.
Description of Related Art
In recent years, there has been a strong demand for development of a small and lightweight secondary battery having a high energy density because of the widespread use of mobile phones and portable devices such as laptop computers. Examples of such a secondary battery include lithium-ion secondary batteries using, as a negative electrode, lithium, a lithium alloy, a metal oxide, or carbon, and such lithium-ion secondary batteries have been actively researched and developed.
A lithium-ion secondary battery using, as a positive electrode active material, a lithium-metal composite oxide, especially a lithium-cobalt composite oxide, can achieve a 4 V-class high voltage, and is therefore expected to serve as a battery having a high energy density. For this reason, the commercialization of such a lithium-ion secondary battery has been accelerated. Many attempts have hitherto been made to develop a battery using a lithium-cobalt composite oxide to achieve excellent initial capacity characteristic and cycle characteristic, and as a result, various results have already been obtained.
Major examples of a positive electrode active material that have hitherto been proposed include a lithium-cobalt composite oxide (LiCoO2) that is relatively easily synthesized, a lithium-nickel composite oxide (LiNiO2) or a lithium-nickel-cobalt-manganese composite oxide (LiNi1/3CO1/3Mn1/3O2) using nickel cheaper than cobalt, and a lithium-manganese composite oxide (LiMn2O4) using manganese, and spherical or almost spherical particles thereof, which are easily synthesized, are mainly used.
The main characteristics of a battery using such a positive electrode active material are a capacity and a power density. Particularly, a battery for hybrid cars, whose demand has significantly increased in recent years, is required to have a high power density.
The power density of a secondary battery can be increased by, for example, reducing the thickness of an electrode film used in the battery. For example, a battery for hybrid cars uses an electrode film having a thickness of about 50 μm. This is because the migration distance of lithium ions in the battery for hybrid cars can be reduced by reducing the thickness of the electrode film. A positive electrode active material for use in such a thin electrode film may penetrate the electrode film, and is therefore limited to small-diameter particles having a uniform particle size. In the case of an electrode film of a battery for hybrid cars, particles having a particle size of about 5 μm are used.
However, the use of such small-diameter particles in an electrode film has a drawback that an electrode density is reduced so that a volume energy density is reduced which is an important characteristic in addition to a power density.    Patent Document 1: JP 2012-84502 A